1. Field of the Invention
The present invention relates to an optical pickup actuator and an optical recording and/or reproducing apparatus. More particularly, the present invention relates to an optical pickup actuator which has an object lens mounted therein and drives the object lens to record and/or reproduces information on and/or from an optical information storage medium, and an optical recording and/or reproducing apparatus employing the same.
2. Description of the Related Art
Conventionally, a digital versatile disk (DVD) uses a laser at 650 nm (or 635 nm) wavelength and an object lens having an aperture of 0.6 (0.65 in case of recordable object lens) to record and/or reproduce data. If the DVD has a diameter of 120 mm and a track pitch of 0.74 um, it has a recording capacity of 4.7 GB per one side.
Therefore, a DVD is not appropriate for recording of motion picture information of high definition (HD) grade. This is because a recording capacity of 23 GB or more is required per one side of a disc sufficiently to record motion picture information having a running time of 135 minutes in high definition.
In order to satisfy the demand for the high-density recording capacity, a blue laser which has a shorter wavelength than a red laser and an object lens having an apeture larger than 0.6 is used. Also, the developments of high-density optical disks having a narrower track, that is, high definition DV (HD-DVD) and standardization therefore have been promoted.
Meanwhile, in order to guarantee a tolerance due to tilting of an optical disk, a thickness of the optical disk must be decreased because the f-number of aperture of an object lens increases to accommodate high density. Considering an allowable tolerance due to the tilting of the optical disk, a CD must decrease to be 1.2 mm thick and a DVD must decrease to be 0.66 mm thick. Thinness of an HD-DVD may be on the order of 0.1 mm. The f-numbers of apertures of object lenses increase to 0.45 and 0.6 for a CD and a DVD, respectively. In the case of HD-DVD, the f-number of an aperture of an object lens may be on the order of 0.85. Also, the HD-DVD may use a celadon green laser in consideration of its recording capacity. However, one of the main problems in developing a new standard optical disk is whether the new optical disk is compatible with existing optical disks.
A sophisticated technique is required to design and fabricate an object lens having a large aperture such as 0.85. Also, making working distance of the object lens having the large aperture as long as that of an object lens for a DVD is difficult.
Therefore, a compatible optical pickup capable of high-density recording/reproduction which has both at least one object lens for recording/reproducing data on a CD and/or DVD and an object lens having a large aperture for high-density recording is required.
On the other hand, an optical pickup actuator requires a magnetic circuit to be moved both in a focusing direction and a track direction, so that the optical pickup actuator is moved in the focusing direction such that a distance between an optical disk and an object lens is constantly maintained, and moved in the track direction to move an object lens to a desirable track position (track center).
As described above, if an optical pickup is to be configured to accommodate a plurality of optical disks having different recording density, it requires object lenses corresponding to the plurality of optical disks. Therefore, an actuator applied to the optical pickup employing the plurality of object lenses requires a magnetic circuit that is capable of driving at least one object lens mounted in a driving part in a focusing direction, a track direction and a tilt direction, and simultaneously maintaining a high sensitivity.